System and method for detecting presence of an infusion cartridge in an infusion pump

ABSTRACT

Infusion devices, systems, and methods can detect a presence or absence of an infusion cartridge in an infusion pump. Embodiments may include a loading sequence, recording loading pulse width modulation (PWM) commands applied to an infusion pump motor during the loading sequence, setting a value of threshold PWM commands based on the commands applied during the loading sequence and comparing values of operational PWM commands applied during pumping operations to the value of the threshold PWM commands. If the value of the operational PWM commands drops below the threshold by a predetermined amount, a missing infusion cartridge warning may be generated.

BACKGROUND

There are many applications in academic, industrial, and medical fields,as well as others, that benefit from devices and methods that arecapable of accurately and controllably delivering fluids, includingliquids and gases that have a beneficial effect when administered inknown and controlled quantities. Such devices and methods areparticularly useful in the medical field where treatments for manypatients include the administration of a known amount of a substance atpredetermined intervals.

Insulin-injecting pumps have been developed for the administration ofinsulin for those suffering from both type I and II diabetes. Continuoussubcutaneous insulin injection and/or infusion therapy with portableinfusion device has been adapted for the treatment of diabetes. Suchtherapy may include the regular and/or continuous injection or infusionof insulin into the skin of a person suffering from diabetes and offeran alternative to multiple daily injections of insulin by an insulinsyringe or an insulin pen. Such pumps can be ambulatory/portableinfusion pumps that are worn by the user that may use replaceablecartridges. Examples of such pumps and various features that can beassociated with such pumps include those disclosed in U.S. patentapplication Ser. No. 13/557,363, U.S. patent application Ser. No.12/714,299, U.S. patent application Ser. No. 12/538,018, U.S.Provisional Patent Application No. 61/655,883, U.S. Provisional PatentApplication No. 61/656,967 and U.S. Pat. No. 8,287,495, each of which isincorporated herein by reference.

There are, however, some drawbacks associated with the use ofsubcutaneous injection syringes and/or some currently available infusionpumps for the delivery of insulin and other medicaments. Somecommercially available pumps may have an interchangeable infusioncartridge containing insulin and/or other medicaments. The correctattachment of this interchangeable infusion cartridge is important forthe proper delivery of medicament. For instance, the cartridge mayinadvertently become detached or may not be attached to the pump,resulting in possible inaccuracies in treatment and other issues.

Therefore, there is a need for a system and a method for detecting thepresence or absence of the infusion cartridge in the infusion pump.

SUMMARY

Disclosed herein are systems and methods for detecting the presence ofan interchangeable infusion cartridge in an infusion pump andparticularly in a portable or ambulatory infusion pump. In someembodiments, the method may include installing an infusion cartridge inan infusion pump, initiating an infusion cartridge loading sequence,recording loading pulse width modulation (PWM) commands applied to aninfusion pump motor, setting a value of threshold PWM commands,comparing values of operational PWM commands applied during pumpingoperations to the value of the threshold PWM commands, and generating amissing cartridge indication whenever the value of an operational PWMcommand drops below the value of the threshold PWM commands by apredetermined amount.

In some embodiments an infusion system is provided. The infusion systemmay be configured for detecting a presence or absence of an infusioncartridge. The infusion system may include an infusion cartridge and aninfusion pump. The infusion cartridge may include a delivery mechanismfor effectuating delivery of fluid having an axial bore, a spool whichmay be disposed within the axial bore and axially translatable withinthe axial bore, and a drug delivery reservoir for storing fluid. Theinfusion pump may include a drive mechanism and a processor. Theprocessor may be coupled to a memory configured for receiving input datafrom the memory and using input data for generating operationalparameters for the infusion system. Programming may be stored in thememory for execution by a processor to control a closed-loop motorcontrol algorithm. The closed-loop motor control algorithm may beconfigured for generating PWM commands that operate a motor of the drivemechanism, and to indicate an absence of the infusion cartridge if thevalue of the operational PWM command falls below the predetermined valuethe threshold PWM commands.

Certain embodiments are described further in the following description,examples, claims, and drawings. These features of embodiments willbecome more apparent from the following detailed description when takenin conjunction with the accompanying exemplary drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart illustrating a method embodiment for detecting thepresence of an interchangeable infusion cartridge in an infusion pump.

FIG. 2 is an exploded view of an embodiment of an infusion cartridge andan infusion pump with the infusion cartridge removed from the infusionpump.

FIG. 3 is a block diagram representing an embodiment of an infusionpump.

FIG. 4 is an elevation view in partial section of a delivery mechanismembodiment of the infusion cartridge embodiment of FIG. 2 coupled to adrive mechanism embodiment.

DETAILED DESCRIPTION

Provided herein are systems, devices and methods for continuous orsemi-continuous monitoring of the absence or presence of aninterchangeable infusion cartridge in an infusion pump, and particularlyin a portable or ambulatory infusion pump utilizing a replaceablecartridge containing insulin and/or other medicaments for the treatmentof diabetes. Some embodiments may include advances in the internalcomponents, the control circuitry, and improvements in a user interfaceof the systems and devices. The advances may allow for a safer and moreaccurate delivery of medicament to a patient than is currentlyattainable today from other devices, systems, and methods. Althoughembodiments described herein may be discussed in the context of thecontrolled delivery of insulin, delivery of other medicaments,including, for example, glucagon, pramlintide, etc., as well as otherapplications are also contemplated, other applications are alsocontemplated. Device and method embodiments discussed herein may be usedfor pain medication, chemotherapy, iron chelation, immunoglobulintreatment, dextrose or saline IV delivery, or any other suitableindication or application. Non-medical applications are alsocontemplated.

It should be noted that labels associated with operations describedherein do not necessarily represent an order in a sequence; rather, theyare used only to uniquely identify each operation. The words “loaded”,“written”, and “programmed” are used interchangeably in this documentwhen they refer to a processor or a memory device. The terms “pump” and“infusion pump” may be used interchangeably throughout the document asmay be the terms “fluid” and “liquid medicament.” In addition, the terms“pulse width modulation (PWM) commands” and “PWM commands”interchangeably represent a series of electrical pulses provided topower an electric motor of the infusion pump. A value, of PWM commandsgenerally represents a duty cycle of the series of pulses during acommand sequence. For example, if the PWM is 100% with an input voltageof 3.0 volts, the output will be 3.0 volts. If the PWM command is 50%,the output voltage of the same 3.0 volt input would be 1.5 volts.

FIG. 2 depicts an embodiment of an infusion pump system 100 with aninfusion cartridge 16 detached from the full-featured infusion pumpdevice 12. The pump 12 can include an attachment mechanism 64,positioned within the first receiving slot 22 that corresponds to areceiving mechanism 62 at an end of the infusion cartridge 16. Theattachment and receiving mechanisms can be configured to removablycouple to each other to provide for an interchange of cartridges withinthe slot 22. The coupling keeps an interior of the cartridge andinterior of the pump sealed from the surrounding environment such thatfluid is retained within the volumes even under significant pressure.This attachment embodiment may be configured to produce a leak freedetachable coupling that can withstand significant pressure. Thereceiving mechanism 62 may be configured to detachably couple with theattachment mechanism 64 such that the infusion cartridge 16 may beremovably attached to the housing 26 of the infusion pump 12 for fluiddelivery. In this embodiment, the attachment mechanism 64 may include apneumatic tap 66 having an O-ring or other sealing device. Thecorresponding receiving mechanism 62 may include a port through whichthe pneumatic tap 66 may be inserted. A reservoir fill port 76 may bedisposed on a top portion of the infusion cartridge 16. In some cases,the desired fluid may be manually dispensed from the interior volume ofa syringe or other source, through the reservoir fill port 76 and intothe interior volume of the infusion cartridge 16.

FIG. 3 illustrates a block diagram of some features that may beincorporated within the housing 26 of the infusion pump 12. The infusionpump 12 may include a memory device 30, a transmitter/receiver 32, analarm 34, a speaker 36, a clock/timer 38, an input device 40, aprocessor 42, a user interface such as a graphical user interface (GUI)60 having a touch sensitive screen 46 with input capability, a drivemechanism 48, and an estimator device 52. The memory device 30 may becoupled to the processor 42 to receive and store input data, and tocommunicate that data to the processor 42. The input data may includeuser input data and sensor input data. The input data from the memorydevice 30 may be used to generate operational parameters for theinfusion pump 12. The GUI 60 may be configured for displaying a requestfor the user to input data, for receiving user input, data in responseto the request, and communicating that data to the memory. The GUI 60can also be configured to display a missing infusion cartridgeindication/warning as discussed herein.

The processor 42 can function to control the overall operation of thepump. Processor 42 may communicate with and/or otherwise control thedrive mechanism, output/display, memory, transmitter/receiver, and thelike. Processor 42 of the infusion pump may communicate with a processorof another device, such as a continuous glucose monitor, a remotecontroller/commander, etc. Processor 42 may include programming that cancontrol the infusion of insulin or other medicament from the cartridge,the data, to be displayed by the display, the data to be transmitted viathe transmitter, etc. Part of the programming may be configured tocontrol an electric motor 170 depicted in FIG. 4. Processor 42 may alsoinclude programming that may allow the processor to receive signalsand/or other data from an input device, such as a sensor sensingpressure, temperature, and the like. The processor 42 may be included asa part of infusion pump 12 or may be used in conjunction therewith.

According to an embodiment, a motor control program may be stored in thememory 30 for retrieval by the processor 42 to operate a closed-loopmotor control algorithm. The closed-loop motor control algorithm may beconfigured for generating PWM commands. The PWM commands may be, e.g., aseries of uniform amplitude voltage pulses that are used to measure thecommand input into the motor. The PWM commands may be coupled, to theelectric motor 170 to power a drive mechanism 48. An embodiment of themotor control algorithm may be a velocity loop algorithm. Such avelocity loop algorithm can be a proportional-integral-derivative (PID)loop in which motor velocity is the controlled output. A value of thePWM commands may be proportional to a load on the electric motor 170.The load may differ greatly, depending on the presence or absence of aninfusion cartridge 16. In the case where the infusion cartridge 16 isabsent, a smaller load may indicate this absence.

The processor 42 may also include additional programming to allow theprocessor 42 to learn user preferences and/or user characteristicsand/or user history data. For instance, to implement changes in use,suggestions based on detected trends, such as, weight gain or loss, andmay include programming allowing the device to generate reports, such asuser history, compliance, trending, and/or other such data.Additionally, infusion pump embodiments of the disclosure may include a“power off” or “suspend” function for suspending one or more functionsof the device, such as, suspending a delivery protocol, and/or forpowering off the device or the delivery mechanism thereof. For someembodiments, two or more processors may be used for controller functionsof the infusion pumps, including a high power processor and a low powerprocessor used to maintain programming and pumping functions in lowpower mode in order to, e.g., save battery life.

Housing 26 of the infusion pump 12 may be functionally associated withan interchangeable and a removable glucose meter 20 and/or infusioncartridge 16. The infusion cartridge 16 may have an outlet port 54 thatmay be connected to an infusion set (not shown) via an infusion setconnector 18 (as shown in FIG. 2).

Referring now to FIG. 1, a flowchart depicting a top-level view of amethod 200 according to embodiments of the present disclosure isillustrated. The method 200 includes detecting the presence or absenceof an infusion cartridge in an infusion pump. In some cases method 200may include two phases, a calibration phase 210 and a pumping phase 220.

Method 200 may start the PWM calibration phase 210 at operation S211. Inoperation S211, an infusion cartridge may be installed in an infusionpump such as, for example, as described above. In operation S212, aninfusion cartridge loading sequence may be initiated. During the loadingsequence an electric infusion pump motor, propelling a chive mechanism,may engage a fluid delivery mechanism within the infusion cartridge. Theengaged fluid delivery mechanism may represent a specific load on theinfusion pump motor. In operation S213, PWM commands applied on theinfusion pump motor during the loading sequence may be recorded intomemory. For example, the PWM commands may have a percent/value rangingfrom 20% to 80%. In operation S214, an average value of the recorded PWMcommands may be calculated. In operation S215, a value threshold of thePWM commands may be set to be the average value of the recorded PWMcommands may be, for example, 52%. Because the PWM configurationprocedure 210 can be clone each time a cartridge is loaded, thethreshold can be set at an appropriate value for each specificcartridge. This is advantageous because the load that each cartridgeimparts on the motor can vary greatly.

After a threshold value has been established for a particular cartridge,a pumping phase 220 can be begun. In operations S221 and S222, duringthe pump phase 220, applied values of the operational PWM commands maybe recorded and the average values of those operational PWM commands maybe calculated. The PWM commands can be recorded and averaged for theduration of each distinct motor move. In operations S223 and S224,during each subsequent motor move in a pumping cycle, the average valueof the operational PWM commands may be compared to the threshold valueof the PWM commands. For example, the average value may be somewherebetween 40% and 90%.

If an average value of the operational PWM commands is smaller, by apredetermined amount, than the value of the threshold PWM commands, amissing infusion cartridge indication/warning may be generated inoperation 225, and the pumping may be halted. In some embodiments, theaverage value of more than one motor move must deviate from thethreshold to generate an alarm. In one embodiment, the alarm isgenerated if two motor moves in a row generate an average PWM valuegreater that deviate from the threshold by the predetermined amount. Incertain embodiments, the number of motor move values that must cross thethreshold to generate an alarm can be adjusted to vary the sensitivityof the alarm. If an average value of the operational PWM commands islarger, by the predetermined value, than the value of threshold PWMcommands, the pumping may continue in operation 221. In one example, thepredetermined amount may be 10%. Thus, in the example in which thethreshold value was 52%, of the average value of the operationalcommands is below 42%, the alarm is generated.

The predetermined value may be selected and set differently based on aselected pumping speed. For example, for a low pumping speed thepredetermined value may be in the range of 20%-40% of the value of thethreshold PWM command, for a high pumping speed the predetermined valuemay be in the range of 40%-60% of the value of the threshold PWMcommand, in one embodiment, this loop 220 can be conducted continuouslyin order to indicate that a cartridge is absent as soon as possible whena cartridge. Is dislodged or removed.

FIG. 4 depicts an embodiment of portion of an infusion cartridge such asinfusion cartridge 16 including the delivery mechanism 120, as well as aportion of the drive mechanism 48 of an infusion pump such as infusionpump 12 with which the method 200 described above can be employed. Thedelivery mechanism 120 may be configured to deliver fluid from acollapsible drug delivery reservoir 68 via a collapsible or variablevolume element of a spool 106. For the embodiments discussed herein, thevariable volume elements may include constrained variable volumeelements that are mechanically constrained to vary between a minimumvolume and a maximum volume. The delivery mechanism 120 may include adelivery mechanism body 102, or housing, and an axial bore 104 disposedin the delivery mechanism body 102. The axial bore 104, may have asubstantially round transverse cross section that may include a distalend 144, a proximal end 148 disposed towards the drive mechanism 48 ofthe infusion pump system 100, a reservoir inlet port 108, a fluid outletport 114, a vent inlet port 112, and a vent outlet port 116. The spool106 may also have a substantially round transverse cross section, whichmay be slidingly disposed within the axial bore 104 and may form aconstrained variable volume 122 and a second vented volume 154 with theaxial bore 104. The drive mechanism 48 may include a rack and pinionmechanism 174 actuated by an electric motor 170 through a gear box 172.

The constrained variable volume 122 of the delivery mechanism 120 may bepositionable to overlap the reservoir inlet port 108 independent of anoverlap of the fluid outlet port 114. The constrained variable volume122 may be formed between a first seal 140 around the spool 106, asecond seal 142 around the spool 106, an outer surface of the spool bodybetween the first and second seal 140 and 142 and an interior surface ofthe axial bore 104 between the first and second seal 140 and 142. Thefirst and second seals 140 and 142 are axially moveable, relative toeach other so as to increase a volume of the constrained variable volume122 when the first and second seals 140 and 142 are moved away from eachother, and decrease the constrained variable volume 122 when the firstand second seals 140 and 142 are moved closer together.

The second seal 142 may be disposed on a proximal section 134 of thespool 106 and may move in conjunction with movement of the proximalsection 134 of the spool 106. A proximal end of the spool 136 may becoupled to a ball portion 178 of a drive shaft 176 of the drivemechanism 48 of the infusion pump 12. The drive mechanism 48 may includea rack and pinion mechanism 174 actuated by an electric motor 170through a gear box 172. As such, the second seal 142 may move ortranslate axially in step with axial translation of the spool 106 anddrive shaft 176. The first seal 140, however, may be disposed on adistal section 128 of the spool 106 which may be axially displaceablewith respect to the main section 190 of the spool 106. The distalsection 128 of the spool 106 may be coupled to the main section of thespool by an axial extension 156 that may be mechanically captured by acavity 158 in the main section 132 of the spool 106. This configurationmay impart a predetermined amount of controlled axial movement betweenthe distal section 128 of the spool and the main section 132 of thespool 106 and may translate the constrained variable volume 122 from thereservoir inlet port 108 to the fluid outlet port 114. Thisconfiguration may expand or contract the constrained variable volume 112of the spool 106 by exerting translational axial force through aboundary section of the constrained variable volume 122.

For some embodiments, a volume of a “bucket” of fluid dispensed by acomplete and full dispense cycle of the spool 106 may be approximatelyequal to the cross-sectional area of the axial bore 104 multiplied bythe length of displacement of the captured axial extension of the spoolfor the distal section 128. The complete bucket of fluid may also bedispensed in smaller sub-volumes in increments as small as a resolutionof the drive mechanism 48 allows. For some embodiments, a dispensevolume or bucket defined by the constrained variable volume 122 of thedelivery mechanism 120 may be divided into about 10 to about 100sub-volumes to be delivered or dispensed. In some cases, the maximumaxial displacement between the distal section 128 and main section ofthe spool 132 may range from about 0.01 inch to about 0.04 inch; morespecifically, from about 0.018 inch to about 0.022 inch.

For some embodiments, the axial bore 104 of the delivery mechanism mayhave a transverse dimension or diameter ranging from about 0.04 inchesto about 0.5 inches; more specifically, from about 0.08 inches to about0.15 inches. For some embodiments, the spool 106 may have a lengthranging from about 10 mm to about 40 mm; more specifically, from about15 mm to about 20 mm. The spool 106 and housing of the deliverymechanism 48 may be made from any suitable material or materials,including polymers or plastics such as polycarbonate, PEEK,thermoplastics, cyclic olefin copolymer, and the like. In some cases,the seals disposed on the spool may have an outer transverse dimensionor diameter that may be slightly larger than that of the spool 106. Insome instances, the seals on the spool may have an axial thicknessranging from about 0.01 inches to about 0.03 inches and may be made frommaterials such as butyl, silicone, polyurethanes or the like having ashore hardness ranging from about 65 A. to about 75 A and, morespecifically, about 70 A.

In some instances, a second vented volume 154 of the delivery mechanism120 may be formed by the spool 106 and axial bore 104 of the deliverymechanism 48. The second vented volume 154 may be formed by a third seal150 disposed around the spool 106 and a fourth seal 152 also disposedaround the spool and axially separated from the third seal 150. Theaxial separation between the third and fourth seals 150 and 152 formingthe second vented volume 154 may be greater than the axial separationbetween the vent inlet port 112 and vent outlet port 116 of the axialbore 104 in some instances. The second vented volume 154 may be formedby an outside surface of the spool 106 between the third and fourthseals 150 and 152 and an inside surface of the axial bore 104 betweenthe third and fourth seals 150 and 152.

The second vented volume 154 may be axially displaceable with themovement of the spool 106 and may also be positionable by such axialdisplacement in order to simultaneously overlap the second vented volume154 with the vent inlet port 112 and the vent outlet port 116 of theaxial bore 104. Such an overlap of both the vent inlet port 112 and thevent outlet port 116 may put these ports in fluid communication witheach other, and may allow an equilibration of pressure between the firstvented volume 80 of the infusion cartridge 16 and the environmentsurrounding the vent outlet port 116. In most cases, the vent outletport 116 may be in communication with the atmosphere and air may passfrom the environment surrounding the vent outlet port 116, through thesecond vented volume 154 of the axial bore 104, and into the firstvented volume 80 to replace the fluid dispensed subsequent to the lastvent cycle. When the vent inlet port 112 and vent outlet port 116 do notshare a common volume formed by the spool 106 and axial bore 104 of thedelivery mechanism 120, they are typically isolated and no venting ofthe first vented volume 80 may take place.

In operation, the spool 106 defines one or more volumes between thespool 106, the axial bore 104 and the circumferential seals 140, 142,150 and 152 disposed on the spool of the delivery mechanism 120. Thespool 106 is typically translated in a proximal and distal direction inorder to move the volumes into and out of communication with the variousports of the axial bore 104. This axial movement in alternating proximaland distal directions of the spool 106 within the axial bore 104 may beused to put the various ports in fluid communication with translatablevolumes of the delivery mechanism 120. For reliable operation, it may bedesirable in some circumstances for the spool 106 and thecircumferential seals 140, 142, 150 and 152 disposed about the spool 106to move smoothly within the axial bore 104 of the delivery mechanism 120while maintaining a seal between an outside surface of the spool 106 andan inside surface of the axial bore 104. It may also be desirable forthe circumferential seals 140, 142, 150 and 152 disposed on the spool106 to move axially back and forth within the axial bore 104 whilemaintaining a seal and with a minimum of friction. Achieving thesefeatures of the spool 106 may be facilitated with the use of particularseal configurations or gland configurations used to house the seals ofthe spool embodiments.

The delivery mechanism 120 may be configured to deliver fluid from thereservoir 68. The delivery mechanism 120 may include a deliverymechanism body 102, or housing, and the axial bore 104 disposed in thedelivery mechanism body 102. The axial bore 104 may have a substantiallyround transverse cross section. The spool 106 may also have asubstantially round transverse cross section, and may be slidinglydisposed within the axial bore 104. The drive mechanism 48 may include arack and pinion mechanism 174 actuated by an electric motor 170 througha gear box 172.

With regard to the above detailed description, like reference numeralsused therein may refer to like elements that may have the same orsimilar dimensions, materials, and configurations. While particularforms of embodiments have been illustrated and described, it will beapparent that various modifications can be made without departing fromthe spirit and scope of the embodiments herein. Accordingly, it is notintended that the invention be limited by the forgoing detaileddescription.

The entirety of each patent, patent application, publication, anddocument referenced herein is hereby incorporated by reference. Citationof the above patents, patent applications. publications and documents isnot an admission that any of the foregoing is pertinent prior art, nordoes it constitute any admission as to the contents or date of thesedocuments.

Modifications may be made to the foregoing embodiments without departingfrom the basic aspects of the technology. Although the technology mayhave been described in substantial detail with reference to one or morespecific embodiments, changes may be made to the embodimentsspecifically disclosed in this application, yet these modifications andimprovements are within the scope and spirit of the technology. Thetechnology illustratively described herein may suitably be practiced inthe absence of any element(s) not specifically disclosed herein. Theterms and expressions which have been employed are used as terms ofdescription and not of limitation and use of such terms and expressionsdo not exclude any equivalents of the features shown and described orportions thereof and various modifications are possible within the scopeof the technology claimed. Although the present technology has beenspecifically disclosed by representative embodiments and optionalfeatures, modification and variation of the concepts herein disclosedmay be made, and such modifications and variations may be consideredwithin the scope of this technology.

What is claimed is:
 1. A method for detecting a presence of an infusioncartridge in an infusion pump, comprising: installing an infusioncartridge in an infusion pump; initiating an infusion cartridge loadingsequence; recording loading pulse width modulation (PWM) commandsapplied to an infusion pump motor during the loading sequence; setting avalue of threshold PWM commands; comparing values of operational PWMcommands that are applied during pumping operations to the value of thethreshold PWM commands; and generating a missing cartridge indication ifthe value of the operational PWM commands drop below the value of thethreshold PWM commands by a predetermined amount.
 2. The method of claim1 wherein the value of threshold PWM commands is an average value of theloading PWM commands.
 3. The method of claim 1 wherein values ofoperational PWM commands are average values of PWM commands of eachsubsequent motor move during a pumping cycle.
 4. The method of claim 1,wherein the PWM commands are uniform amplitude voltage pulses.
 5. Themethod of claim 1, where the predetermined amount is based on a pumpingspeed of the pumping operations.
 6. The method of claim 1 wherein thepredetermined amount is between 20% and 40% of the threshold.
 7. Themethod of claim
 1. wherein the predetermined amount is between 40% and60%.
 8. An infusion system configured for detecting a presence of aninfusion cartridge, comprising: an infusion cartridge comprising: adelivery mechanism for effectuating a delivery of fluid, the deliverymechanism including; an axial bore, and a spool disposed within theaxial bore and axially translatable within the axial bore, and a drugdelivery reservoir for storing fluid; and an infusion pump comprising: adrive mechanism including a motor operatively coupleable to the spooland configured to impart controlled axial movements of the spool thatmove fluid from the infusion cartridge to an outlet port; a processor,the processor coupled to a memory configured for receiving input datafrom the memory and using input data for generating operationalparameters for the infusion system; the memory adapted to receive andstore input data coupled to the processor and configured forcommunicating that data to the processor; and programming stored in thememory for retrieval by the processor to control a closed loop motorcontrol algorithm, the closed loop motor control algorithm configured togenerate pulse width modulation (PWM) commands to operate the motor ofthe drive mechanism, wherein when values of the PWM commands fall belowa threshold value by a predetermined amount an absence of the infusioncartridge warning is generated.
 9. The infusion system of claim 8,further comprising a user interface configured for displaying a requestfor a user to input data, wherein the display is further configured forreceiving user input data in response to the request and communicatingthat data to the memory.
 10. The infusion system of claim 9, wherein theuser interlace is further configured to display the absence of theinfusion cartridge warning.
 11. The infusion system of claim 8, in whichthe closed loop motor control algorithm is a velocity loop algorithm.12. The infusion system of claim 8, in which value of the PWM commandsis proportional to a load on the motor of the drive mechanism.
 13. Theinfusion system of claim 8, wherein the threshold value is determinedbased off of PWM commands applied to the pump motor during a loadingsequence of an infusion cartridge.
 14. The infusion system of claim 8,wherein the PWM commands are uniform amplitude voltage pulses.
 15. Theinfusion system of claim 8, where the predetermined amount is based on apumping speed of the pumping operations.
 16. A method of calibrating aninfusion pump that utilizes an infusion cartridge, comprising:installing an infusion, cartridge in an infusion pump; initiating aninfusion cartridge loading sequence; recording loading pulse widthmodulation (PWM) commands applied to an infusion pump motor during theloading sequence; and setting a value of threshold PWM commands.
 17. Themethod of claim 16, wherein the value of threshold PWM commands is anaverage value of the loading PWM commands.
 18. The method of claim 16,wherein the PWM commands are uniform amplitude voltage pulses.
 19. Themethod of claim 16, wherein the threshold value is variable based on aspeed of subsequent pumping operations of the infusion pump.